Copper catalysts

ABSTRACT

A copper oxide/zinc oxide/aluminium oxide catalyst which contains, per 100 parts of copper oxide, 40 to 130 parts zinc oxide, 2 to 50 parts aluminium oxide, and 1 to 4 parts soium oxide. It has a total BET surface area of 50 to 100 m 2  /g, and 75% to 95% of the total surface area is made up by pores having radii of 9 to 1000 nm, and 5% to 25% of the total surface area is made up by pores having radii of less than 9 nm. The catalyst is useful for hydrogenation of various organic compounds.

This Application claims the benefit of priority of German Application P42 44 273.7, filed Dec. 28, 1992.

The invention relates to a novel catalyst which, in addition to copperoxide, comprises zinc oxide and aluminum oxide, and to a process for itspreparation. Because of its high activity and selectivity, the catalysthas proven useful in the hydrogenation of organic compounds, inparticular saturated or unsaturated aldehydes, ketones, carboxylicacids, and carboxylic esters to form saturated alcohols.

BACKGROUND OF THE INVENTION

Copper-containing catalysts have wide application in chemicaltechnology. Depending on the specific use to which they are put, theydiffer primarily in the materials which they contain and thequantitative composition thereof. Specifically, copper oxide/zincoxide/aluminum oxide catalysts are the basis of modern processes forsynthesizing methanol from carbon monoxide and hydrogen at lowpressures.

For instance, DE-A-20 56612 describes catalysts for preparing methanolwhich are compounds of the mixed crystal series (Cu_(x) Zn_(y))Al₂(OH)₁₆ CO₃.4H₂ O, where x and y are 0.5 to 5.5 and the sum of x and y is6. The desired mixed crystals are obtained by reaction of aqueoussolutions containing copper nitrate, zinc nitrate, and aluminum nitratewith basic reagents, such as aqueous sodium carbonate solution, at pHvalues of 4.5 to 5.5.

EP-A-01 25 689 also relates to copper oxide/zinc oxide/aluminum oxidecatalysts for methanol synthesis. They are characterized by a Cu/Znatomic ratio of 2.8 to 3.8 and an Al₂ O₃ content of 8% to 12% by weight.They are prepared by coprecipitating copper and zinc with alkalinematerials, such as alkali metals or ammonium carbonate, in the presenceof the aluminum oxide component, preferably colloidally dispersedaluminum oxide or hydroxide, from their aqueous solutions. In theunreduced catalyst, 20% to 40% of the pores have a radius of from 1.0 to3.75 nm and from 60% to 80% of the pores have a radius greater than 3.75nm.

A further application for the above compositions is hydrogenation oforganic compounds. For this type of reaction, CuO/ZnO/Al₂ O₃ catalystsreplace copper/chromium oxide catalysts (known as Adkins catalysts), theuse of which has been avoided in recent times for ecological reasons,and they are in competition with the multiplicity of nickel catalystswhich have been described and introduced to industry.

Hydrogenation catalysts based on copper oxide, zinc oxide and aluminumoxide wherein at least about 80% of their pore volumes consists of poreshaving a diameter greater than about 80 Å (8 nm) are the subject of EP04 24 061. In preferred embodiments, the catalyst powder has a surfacearea of at least 70 m² /g, the average particle diameter is about 8toabout 28 μm and the atomic ratio of copper to zinc is about 0.2 to about5.5. The catalysts are produced by preparing two aqueous solutions, onecontaining copper and zinc salts and the other containing a basicaluminum salt (for example sodium aluminate) and a basic precipitationreagent (for example soda). The two solutions are mixed with one anotherin a ratio such that the pH of the resulting mixture is at least about7. The precipitated solid is subsequently filtered off and calcined. Thecatalyst is used for hydrogenating aldehydes, ketones, carboxylic acids,and carboxylic esters.

The known catalysts containing copper oxide, zinc oxide, and aluminumoxide have frequently been developed specifically for particularreactions; e.g. methanol synthesis or the hydrogenation of organiccompounds. They can nevertheless also be used for other chemicalreactions but, in such cases, do not always produce optimal results.Even different ways of carrying out the same reaction may require theprovision of individualized catalysts. Experience has shown that thereaction of the same reactants under different conditions (for examplein gaseous or in liquid form, on fixed catalysts, or on a catalystsuspended in the substrate) requires specially adapted catalysts. Inthis context it must be remembered that, in processes which are carriedout on a large scale, an increase in conversion or an improvement in theselectivity in the order of even a few tenths of a percent can lead tosignificant economic advantages.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to providecatalysts of high activity and selectivity which can either be used verywidely or be targeted at particular processes or process variants. Inthe specification and claims hereof, all parts and percentages are byweight unless otherwise stated.

This object is achieved by a catalyst comprising, per 100 parts ofcopper oxide, 40 to 130 parts of zinc oxide, 2 to 50 parts of aluminumoxide, and 1 to 4 parts of sodium oxide. The catalyst has a total BETsurface area of 50 to 100 m² /g; 75% to 95% of the total surface areaconsists of pores having radii of 9 to 1000 nm, and the remainder of thetotal surface area consists of pores having radii of less than 9 nm.

The catalyst of the invention has, in comparison with other catalysts ofthe same or similar qualitative compositions, appreciably higheractivity and selectivity. It has proven particularly useful as ahydrogenation catalyst, and is used very successfully, for example, inthe hydrogenation of saturated or unsaturated aldehydes, carboxylicacids, and carboxylic esters to form saturated alcohols.

DETAILED DESCRIPTION OF THE INVENTION

Preferably, the catalyst comprises, per 100 parts of copper oxide, 40 to100, in particular 45 to 80, parts of the zinc oxide; 4 to 30, inparticular 4 to 20, parts of aluminum oxide; and 1.5 to 3 parts ofsodium oxide. The catalyst optionally contains further metals such asmanganese, molybdenum, vanadium, zirconium, and/or an alkaline earthmetal. Calculated as oxides, namely MnO, MOO₃, V₂ O₅, ZrO₂, and MeO (Meis an alkaline earth metal), the proportion thereof is, per 100 parts ofCuO, 0.5 to 8, preferably 1 to 6, most preferably 2 to 4 parts. Theabove amounts given for the metal oxides are only for the analyticaldescription of the catalyst. They do not give the materials of which itis composed in the sense of, for example, sodium actually being presentas Na₂ O and aluminum being present in the form of the chemical compoundAl₂ O₃ .

In addition to the materials of which it is composed, the novel catalystis characterized by its BET total surface area determined by adsorptionof nitrogen. The catalyst of the invention in the calcined state, i.e.after heating for 3 to 10 hours at 350° to 480° C., preferably 400° C.,has a BET surface area of 50 to 100 m² /g, in particular 60 to 80 m² /g.

The novel catalyst is further characterized by a particular porestructure. The proportion of pores having radii of 9 to 1000 nmcomprises 75% to 95% of the total surface area, and the remainder of thetotal surface area consists of pores having radii less than 9 nm.Preferably, the proportion of pores having radii of 9 to 1000 nm is 80%to 90% and the proportion of pores having radii of less than 9 nm is 10%to 20%. Particularly useful are catalysts whose total surface area ismade up to the extent of 55% to 85% by pores having radii of 15 to 1000nm, to the extent of 5% to 25% by pores having radii of from 9 to lessthan 15 nm, and to the extent of 10 to 20% by pores smaller than 9 nm.The above pore sizes are all based on the calcined catalyst.

The pore-radius distribution is determined by two methods whichsupplement each other. The distribution of small radii (up to about 30nm) is determined by evaluation of the N₂ desorption isotherm by meansof the Kelvin equation as described in C. Pierce, J. Phys. Chem. 57(1953), 149 ff. Pore radii of about 4 nm to about 0.1 mm are determinedby the mercury penetration method of H. L. Ritter and L. C. Drake, Ind.Eng. Chem. analyt. Ed. 17 (1945), 782.

Pores of the above size and size distribution can be achieved by a highCO₂ -content (in the form of carbonate) in the catalyst precursor, i.e.in the product dried at from 50° to 95° C. but not yet calcined. It hasproven advantageous for this precursor to contain, per 100 parts ofcopper oxide, 32 to 45, preferably 36 to 40, parts of CO₂.

The novel catalyst can be prepared, for example, by precipitation of thecomponents from an aqueous solution under conditions which ensure thehigh CO₂ -content which is advantageous in the catalyst precursor. Aparticularly suitable process comprises forming an aluminum hydroxidesuspension by reaction of an aluminum salt solution with an alkali metalcarbonate or alkali metal hydrogen carbonate solution, simultaneouslybut separately adding, at 80° to 100° C. while stirring, a solutioncontaining copper and zinc salts and a solution of alkali metalcarbonate or alkali metal hydrogen carbonate. The solid formed isfiltered off, washed, dried at 50° to 95° C., and then calcined at 350°to 480° C. The aluminum, copper, and zinc salts used are compoundsreadily soluble in water which are derived from inorganic or evenorganic acids, such as halides, sulfates, or acetates. Because of theirhigh solubility, their chemical inertness, the comparative ease ofremoval of the anion, and their general availability, nitrates arepreferred. Precipitants used are alkali metal carbonates and/or hydrogencarbonates, in particular their sodium salts. The concentration of thesalts in the solutions may vary over a wide range. The aluminum saltsolution contains, per liter of solution, the aluminum salt in an amountwhich corresponds to 20 to 100, preferably 30 to 90, and in particular40 to 80, grams of Al₂ O₃. The concentrations of copper and zinc intheir joint solution are from 10 to 100 g of Cu and from 5 to 80 g of Znper liter of solution. The preferred precipitant, sodium carbonate, isadvantageously used as a solution which contains 50 to 150 g of Na₂ CO₃per liter; however, the use of lower sodium carbonate concentrations isnot excluded.

The aluminum hydroxide is precipitated by running the aluminum saltsolution at 20° to 90° C. over 2 to 10 minutes into an alkali metalcarbonate and/or alkali metal hydrogen carbonate solution which is at20° to 100° C., preferably 30° to 80° C. while stirring vigorously. Theratio of aluminum salt to precipitant is selected so that the pH of thesuspension is 6.5 to 8.5 after the reaction is complete. Subsequentlythe temperature is adjusted to 80° to 100° C., preferably 90° to 98° C.,and the alkali metal carbonate and/or alkali metal hydrogen carbonatesolution and the copper salt/zinc salt solution, each heated to 80° to100° C., preferably from 90° to 98° C., are added simultaneously butseparately over 10 to 30 minutes while stirring vigorously. The rates ofaddition of the two solutions are adjusted so that the pH of thesuspension is 7.5 to 8.0. As soon as the addition of the two solutionsis complete, the suspension is filtered. The filter residue is washed,dried at 50° to 95° C., and subsequently calcined at 350° to 480° C.,preferably 400° to 460° C. The shaping of the material, for example byextrusion or tableting, can be carried out before drying or aftercalcination. The catalyst is activated by reduction at 130° to 200° C.,preferably 150° to 180° C. The reduction is conducted in a separatereactor or directly in the hydrogenation reactor.

The novel catalyst is successfully used for hydrogenating organiccompounds, preferably for hydrogenating saturated or unsaturatedaldehydes, ketones, carboxylic acids, or carboxylic esters. It hasproven particularly useful in the hydrogenation of unsaturated andsaturated aldehydes in the gaseous phase.

The examples below illustrate the invention, but do not limit it.

EXAMPLE 1 Catalyst preparation

A solution of 925 g of Al(NO₃)₃.9H₂ O in 3 liters of water at roomtemperature is introduced within 3 minutes into a solution heated to 70°C. of 580 g of soda in 5.5 liters of water with vigorous stirring. Whilecontinuing stirring, the temperature of the resulting suspension israised to 95° C. over a period of about

10 minutes. A solution heated to 95° C. of 2249.2 g of Cu(NO₃)₂.3H₂ Oand 1755.4 g of Zn(NO₃)₂.6H₂ O in 10 liters of water and a solution alsoheated to 95° C. of 2340 g of Na₂ CO₃ in 18 liters of water are addedsimultaneously but separately over a period of 15 minutes. During thereaction, the suspension is maintained at a pH of 7.5 to 8.0.Subsequently, the suspension is stirred for a further 2 minutes and thenfiltered. The filter residue is continuously washed for 80 minutes with80 liters of water and, after shaping by extrusion or by spray drying,is dried at no more than 100° C. to a water content of less than 5%. Thedried uncalcined catalyst precursor comprises 38.8% CuO (31% by weightCu). It also contains 65 parts ZnO, 17 parts Al₂ O₃, 2.0 parts Na₂ O,and 38.6 parts CO₂ per 100 parts CuO.

In a subsequent process step, the precursor is heated in a stream ofnitrogen or air (200 liters/h) to 430° C. and maintained at thistemperature for a further 3 hours. The resulting calcined productcomprises 51% CuO, and 65 parts ZnO, 17 parts Al₂ O₃, 2.0 parts Na₂ O,and 1.5 parts CO₂ per 100 parts CuO. It has a total BET surface area of68 m² /g; 84% of the surface area is made up by pores having radiigreater than 9 nm but less than 1000 nm, and 16% is made up by poreshaving radii less than 9 nm. The calcined product can be used inextruded or tableted form as a fixed-bed catalyst.

EXAMPLE 2 Hydrogenation of n-butyraldehyde

250 ml of the catalyst of Example 1 which has been tableted is reducedin a reaction tube at 160° C. with 400 liters/hour of a H₂ /N₂ mixturecontaining 3% by volume of H₂ until no more water is formed.Subsequently, a mixture of 250 ml of gaseous n-butyraldehyde and 710liters of hydrogen per hour are passed over the catalyst at 145 ° C. anda gauge pressure of 0.3 MPa. The excess hydrogen is recirculated.

The hydrogenation product has the following composition, determined bygas chromatography:

    ______________________________________                                        n-butanol            99.8%     by weight                                      n-butyraldehyde                                                                              <     0.05%     by weight                                      butyl butyrate <     0.05%     by weight                                      2-ethylhexanol <     0.05%     by weight                                      di-n-butyl ether                                                                             ≦                                                                            10.0      ppm by weight                                  ______________________________________                                    

Particularly noteworthy in comparison with the prior art is theexceptionally low formation of byproducts when using the catalysts ofthe invention.

EXAMPLE 3 Hydrogenation of 2-ethylhexenal

3 liters of the catalyst of Example 1 which has been tableted is reducedas in Example 2. Subsequently, a gaseous mixture of 1500 ml/h of2-ethylhexenal (liquid) and 4.4 standard m³ /h of hydrogen is passedover the catalyst at 145° C. and a gauge pressure of 50 kPa. Thestarting material and reaction product have the following compositions,determined by gas chromatography.

    ______________________________________                                                     Starting  Reaction                                                            material  product                                                             (% by weight)                                                                           (% by weight)                                          ______________________________________                                        C.sub.7 /C.sub.8 hydrocarbons                                                                ≦0.1 ≦0.1                                        n/i-butanal    3-4         --                                                 n/i-butanol    0.5-1.5     3.5-4.5                                            2-ethylhexenal   90-91.5   0.1                                                2-ethylhexanal about 1     0.2-0.3                                            2-ethylhexanol 3.5-4.5     95-97                                              higher boiling-point                                                                         2-3         0.5-0.8                                            components (such as                                                           acetals, diols)                                                               ______________________________________                                    

EXAMPLE 4 (comparative) Hydrogenation of n-butyraldehyde

In this example, a catalyst of the prior art is used. It comprises 47.5%Cu, and 49.5 parts ZnO, 8.4 parts Al₂ O₃, and 0.12 parts Na₂ O per 100parts CuO. Its total BET surface area is 128 g/m² ; 85% of the surfacearea is made up of pores having radii equal to or less than 15 nm.

250 ml of the tableted catalyst is reduced in a tube reactor, as inExample 2. Subsequently, a gaseous mixture of 250 ml/h ofn-butyraldehyde (liquid) and 710 liters of hydrogen per hour is passedover the catalyst at 145° C. and a gauge pressure of 0.3 MPa. The excesshydrogen is recirculated.

The hydrogenation product has the following composition by gaschromatography:

    ______________________________________                                        n-butanol          99.5-99.6% by weight                                       n-butyraldehyde    0.2-0.3% by weight                                         butyl butyrate     about 0.02% by weight                                      di-n-butyl ether   about 100 ppm by weight                                    ______________________________________                                    

While only a limited number of specific embodiments of the presentinvention has been expressly disclosed, it is, nonetheless to be broadlyconstrued and not to be limited except by the character of the claimsappended hereto.

What we claim is:
 1. A catalyst comprising, per 100 parts copper oxide,40 to 130 parts zinc oxide, 2 to 50 parts aluminium oxide, and 1 to 4parts sodium oxide, said catalyst having a total BET surface area of 50to 100 m^(2/) g, wherein 75% to 95% of said total surface area is madeup by pores having radii of 9 to 1000 rim, the remainder of said totalsurface area being pores having radii of less than 9 nm.
 2. A catalystas claimed in claim 1 comprising, per 100 parts by weight of copperoxide, 40 to 100 parts zinc oxide, 4 to 30 parts aluminium oxide, and1.5 to 3 parts sodium oxide.
 3. The catalyst of claim 2 comprisisng, per100 parts of copper oxide, 45 to 80 parts zinc oxide and 4 to 20 partsaluminium oxide.
 4. The catalyst of claim 1 comprising, per 100 partscopper oxide, 0.5 to 8 parts of a metal selected from the groupconsisting of manganese, molybdenum, vanadium, zirconium, alkalineearths, and mixtures thereof, said metal being calculated as MnO, MoO₃,V₂ O₅, ZrO₂, and MeO, wherein Me is alkaline earth.
 5. The catalyst ofclaim 4 wherein there are, per 100 parts copper oxide, 1 to 6 parts ofsaid metal.
 6. The catalystt of claim 5 wherein there are, per 100 partscopper oxide, 2 to 4 parts of said metal.
 7. The catalyst of claim 1wherein said BET surface area is 60 to 80 m^(2/) g.
 8. The catalyst ofclaim 1 wherein 80% to 90% of said total BET surface area is made up bypores having radii of 9 to 1000 nm and 10% to 20% of said total BETsurface area is made up by pores having radii less than 9 nm.
 9. Thecatalyst of claim 1 wherein 55% to 85% of said total BET surface is madeup by pores having radii of 15 to 1000 nm, 5% to 25% of said total BETsurface area is made up by pores having radii of 9 to less than 15 nm,and 10% to 20% of said ! total BET surface are is made up by poreshaving radii less than 9 nm.
 10. A process for preparing a catalystcomprising, per 100 parts copper oxide, 40 to 130 parts zinc oxide, 2 to50 parts aluminum oxide, and 1 to 4 parts sodium oxide, said catalysthaving a total BET surface area of 50 to 100 m^(2/) g, wherein 75% to95% of said total surface area is made up of pores having radii of 9 to1000 nm, the remainder of ! said total surface area being pores havingradii of less than 9 nm, said process comprising;forming an aluminumhydroxide suspension by a first reaction of an aluminum salt solutionwith a solution comprising an alkali metal carbonate or an alkali metalhydrogen carbonate, simultaneously, but separately adding (1) a firstsolution having a temperature of 80° to 100° C., said first solutioncontaining copper and zinc salts, and (2) a second solution having atemperature of 80° to 100° C., said second solution containing alkalimetal carbonate or alkali metal hydrogen carbonate, to said aluminumhydroxide suspension, thereby causing a second reaction forming a solidas a precipitation suspension, maintaining a pH of 7.5 to 8.0 in saidprecipitation suspension, and filtering said precipitation suspension toseparate out said solid, washing said solid, drying said solid at 50° to95° C. to form a precatalyst, and calcinating said precatalyst at 350°to 480° C.
 11. The process of claim 10 wherein said calcining is at 400°to 460° C.
 12. The process of claim 10 wherein said aluminium saltsolution is at a temperature of 20° to 90° C., said alkali metalcarbonate solution or said alkali metal hydrogen carbonate solution orsaid alkali metal hydrogen carbonate solution is at a temperature of 20°to 100° C., said aluminium salt solution and said alkali metal carbonatesolution or said alkali metal hydrogen carbonate solution being added insuch amounts that the pH of said precipitation suspension, aftercompletion of said second reaction, is 6.5 to 8.5.
 13. The process ofclaim 10 wherein said calcining is carried out for 3 to 10 hours. 14.The process of claim 10 wherein said precatalyst contains, per 100 partscopper oxide, 32 to 45 parts of carbonate calculated as CO₂.
 15. Theprocess of claim 14 wherein, per 100 parts of copper oxide, saidprecipitation suspension contains 36 to 40 parts of carbonate calculatedat CO₂.
 16. The process of claim 10 wherein said salt solution contains20 to 100 g/liter of aluminum oxide.
 17. The process of claim 16 whereinsaid salt solution contains 40 to 80 g/liter of aluminum oxide.
 18. Theprocess of claim 10 wherein said first solution contains 10 to 100g/liter of copper and 5 to 8 g/liter of zinc.
 19. The process of claim18 wherein said second solution contains 50 to 150 g/liter of sodiumcarbonate.